1. Field of the Invention
The present invention relates to electrical circuits and circuit testing, and, in particular, to a method and apparatus for testing electrical circuits for arc fault current and ground fault current anomalies.
2. Description of Related Art
A modern electrical system has a plurality of circuits connected to a circuit overload device such as a circuit breaker or a fuse box. The circuit overload device is connected to a line voltage. The National Electrical Code (NEC) requires all such circuits to be protected from shorts and circuit overloads by a circuit overload device. Conventional circuit breakers and fuse boxes can only isolate a circuit from the line voltage at an appreciable number of amperes (A). Therefore, the danger of fire and electrocution is often present in these circuits, even when properly grounded, because of electrical faults, such as ground fault current leakage or arc fault current leakage, associated with the circuits.
Typically, ground fault or arc fault current leakage occurs when the hot or neutral conductor of the circuit becomes grounded in some manner, i.e., via contact with another wire, mechanical ground wire, pipe, heat ducts, etc. When the electrical fault is not detected by the circuit breaker, a potentially dangerous situation exists. Because arc fault and/or ground fault current does not stay in one location for an extended period of time, the fault current can form an undetected parallel circuit path on a foreign surface and enter a building's grounding system.
Moreover, any increased line voltage from lightning or power surges can worsen a preexisting ground fault or arc fault damage condition. When lightning strikes near a power line it can induce a surge into the utility company main phase conductors serving many homes and buildings. Without notice, the surge can thermally degrade or damage electrical system wiring and components. The increased circuit voltage can start a slow burning process called pyrolysis. When the size of the electrical fault increases many times, the resistance of the circuit is lowered and there is a subsequent rise in current, increased I2R heating, accelerated carbon tracking, and charcoal formation prior to fire ignition.
The mechanical ground wires of a typical electrical system were originally designed for human protection against electrical shock. However, grounding has had an opposite safety effect in modern electrical systems. In approximately 1963, the NEC incorporated a mechanical ground wire system into all types of buildings to protect people against electrical shock. The system tied all metallic building materials in parallel with copper and aluminum grounded circuit wires. Such as a system typically encounters multiple ground fault and arc fault current leakage problems.
In approximately 1953, the first bimetallic circuit breaker was introduced. These bimetallic circuit breakers, still in use today, function to shut off the current supply when the breaker's bimetal strip heats up to a temperature of 125% of its trip rated capacity, e.g., 25 A for a 20 A breaker. However, the standard bimetallic circuit breaker will not detect thermal damage or breakdowns from high resistance series or parallel arcing, current leakage from hot or neutral conductors, and/or current leakage from a faulty appliance which occur in wiring downstream of the electrical panel in which the breaker is situated. Additionally, standard circuit breakers will not detect electrical anomalies occurring from exposed wires, loose wire connections, unbalanced multiple neutral wires sharing a single circuit, and unbalanced multiple breaker circuit feeds. Thus, hysteresis makes the window of safe operation for a conventional circuit breaker highly questionable. Conventional circuit breakers will not detect ground fault or arc fault current leakage due to their limited trip capacity of about 15 A or more. Therefore, electrical anomalies occur and can be undetected in any home or building.
While ground fault circuit interrupters (GFCIs) have been made available since 1973, installers have mistaken ground fault current leakage for nuisance tripping, while compromising millions of installed GFCI devices. GFCIs can detect current leakage from a hot conductor, but they fail to provide the same protection on a neutral conductor. Thus, GFCI protected circuits and appliances are unknowingly leaking ground fault current at dangerous levels and are susceptible to fire if a neutral is opened, polarity is reversed, or I2R heating occurs.
While arc fault circuit interrupters (AFCIs) have been made available since 2002, their use is still in the experimental phase. The 2002 edition of the NEC requires only limited AFCI protection in new construction for bedroom outlet circuits. Thus, many homes and buildings have electrical circuits and appliances which are unprotected or are presently leaking arc fault current at dangerous levels.
Typically, ground fault or arc fault current leakage or arc fault or ground fault arcing occurs when the hot or neutral conductor of a circuit becomes grounded in some manner, (i.e., via contact with another wire, mechanical ground wire, grounded building materials such as wire mesh, aluminum siding, pipes and heat ducts, etc). In other words, an energized (parallel) current path forms on a foreign surface compromising the originating circuit conductor and a building's electrical grounding system. Alternately, an in-series arc fault can occur when a single conductor is broken within a single wire.
Moreover, one result of an energized foreign surface/object is arc tracking and increased carbonization, a major cause of electrical fires. Whereas, carbon is produced from the charcoaling of woods, by graphite brushes or dust in motors and by diamond dust from other sources, the heating from an electrical arc simultaneously leaves a carbon residue on wood, metallic or other conductive surfaces. All three forms of carbon are conductive current carrying conductors.
Whereas, arc tracking and carbonization is a result of pyrolsis from I (squared) R heating, carbon is a consequence of circuit voltage and ground fault or arc fault current leakage/arcing. Therefore, fires occur when circuit heating is sufficient to produce carbon and a temperature near ignition point after voltage is increased at a preexisting ground fault or arc fault, via power surges, lightning or broken neutral service entrance cable. Further, there also should be great concern for reversed circuit polarity.
When circuit voltage is increased from its normal 120 volts to 240 volts, I (squared) R heating becomes four times as great as the normal circuit heating at an electrical fault. Therefore, if 120 volts increases to 480 volts, heating goes up sixteen times, if voltage increases to 960 volts, heating accelerates sixty-four times, and if circuit voltage goes to 1920 volts, heating at an electrical fault increases 256 times and so on.
A 120-volt Ground Fault Circuit Interrupter (GFCI) circuit tester and method as described detects electrical circuit and/or appliance, equipment, and machinery ground fault current leakage and/or parallel ground fault arcing in an amount greater than 5 milliampere.
A 120-volt Arc Fault Circuit Interrupter (AFCI) circuit tester and method detects current leakage and/or parallel arcing on electrical circuits appliances, equipment, and machinery in an amount greater than 50 amperes.
In addition, an approximate 120-volt circuit load and a 120 volt power source also detects in-series arcing in electrical circuits and/or appliances, equipment, and machinery in an amount greater than 5 amperes.
A ground fault measuring 5 milliampere on a conventional circuit of approximately 240 volts will measure 2.5 milliampere if tested with a 120 volt circuit tester and method of the invention. It is therefore necessary to utilize a 240-volt circuit tester and method of the invention in series with a 240-volt circuit being tested.